MIGRATORY BEHAVIOR OF OVIGEROUS BLUE CRABS CALLINECTES-SAPIDUS - EVIDENCE FOR SELECTIVE TIDAL-STREAM TRANSPORT

In the late summer and early fall, newly inseminated female blue crabs (Callinectes sapidus) leave low-salinity areas of estuaries and migra te seaward to spawn near the entrance. We tested the hypothesis that m igration of female C. sapidus to spawning grounds is facilitated by se lective tidal-stream transport (STST). We monitored the swimming direc tion of adult crabs from a stationary platform located about 1 km insi de the entrance to the Newport River Estuary (Beaufort, North Carolina ). Swimming activity near the surface occurred primarily at night and most crabs avoided swimming against tidal currents. Eighty-one percent of the crabs observed moving down-estuary toward the inlet during ebb tide were ovigerous females. Of the 36 gravid females captured travel ling in ebb currents, 97% possessed dark egg masses containing late-st age embryos. Conversely, nearly all (98%) adult crabs observed traveli ng in flood currents lacked egg masses, and all the females captured w hile migrating up-estuary exhibited signs of recent spawning. These ob servations indicate that ovigerous blue crabs use ebb-tide transport t o migrate seaward to spawn and flood-tide transport to reenter the est uary shortly after larval release.